[Pm-utils] unify boolean config variables

[Michael Biebl]

Hi,

currently our man pages and config variables are not very consistent
with regard to boolean variables.

The majority uses true/false,
there is HIBERNATE_RESUME_POST_VIDEO which is yes/no
and NEED_CLOCK_SYNC, where anything else then "" is treated as true
(see 90clock).

I'd like to use true/false for all boolean values and update the
manpages for HIBERNATE_RESUME_POST_VIDEO and NEED_CLOCK_SYNC and also
the check in 90clock, to test explictly [ "$NEED_CLOCK_SYNC" = "true"
] || ...

Any objections? Do you think this would pose upgrade problems for
users who already set
HIBERNATE_RESUME_POST_VIDEO to yes or no ( I could check both values
(yes/no,true/false))

Cheers,
Michael

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